perf(prediction): eliminate provable tail-call contexts - #345
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Classify parser and lexer rule calls whose follow-state closure can only reach the enclosing rule stop through plain epsilon edges. Reuse the existing prediction context for those calls while preserving SLL accuracy by default, and omit equivalent frames when building full caller contexts. Encode parser markers in packed ATN format 3, keep formats 1 and 2 readable, and advance the generated-code API to revision 14 while retaining revisions 12 and 13. Regenerate the checked-in ANTLRv4, Rust, TOML, and XPath recognizers and update compatibility tests and documentation.
Copy/Paste DetectionFound 33 duplication(s) across 10 changed non-generated Rust file(s) (threshold: 100 tokens). Show duplicationsFound a 54 line (320 tokens) duplication in the following files:
atn: &LexerAtn,
hooks: &mut H,
mut generated_action: A,
mut generated_predicate: P,
unknown_policy: UnknownSemanticPolicy,
mut accept_adjuster: E,
) -> Result<TokenId, TokenStoreError>
where
I: CharStream,
H: SemanticHooks,
A: FnMut(&mut BaseLexer<I>, LexerCustomAction) -> bool,
P: FnMut(&BaseLexer<I>, LexerPredicate) -> Option<bool>,
E: FnMut(&mut BaseLexer<I>, i32, usize),
{
let hooks = RefCell::new(hooks);
let token = next_token_with_hooks_impl(
lexer,
sink,
atn,
&mut |lexer, action| {
if !generated_action(lexer, action)
&& !dispatch_lexer_action_hook(&hooks, lexer, action)
&& unknown_policy == UnknownSemanticPolicy::Error
&& let (Ok(rule), Ok(index)) = (
usize::try_from(action.rule_index()),
usize::try_from(action.action_index()),
)
{
lexer.record_semantic_error(true, rule, index);
}
},
&mut |lexer, predicate| {
generated_predicate(lexer, predicate)
.or_else(|| dispatch_lexer_predicate_hook(&hooks, lexer, predicate))
.unwrap_or_else(|| match unknown_policy {
UnknownSemanticPolicy::AssumeTrue => true,
UnknownSemanticPolicy::AssumeFalse => false,
UnknownSemanticPolicy::Error => {
lexer.record_semantic_error(
false,
predicate.rule_index(),
predicate.pred_index(),
);
false
}
})
},
&mut |lexer| dispatch_lexer_before_token_hook(&hooks, lexer),
&mut accept_adjuster,
&mut |lexer, accept_position| {
dispatch_lexer_after_accept_hook(&hooks, lexer, accept_position);
},
LexerMatchStrategy {
compiled: None,
```rust
---
Found a 21 line (226 tokens) duplication in the following files:
* Starting at line 15302 of crates/antlr-rust-runtime/src/parser.rs
* Starting at line 16707 of crates/antlr-rust-runtime/src/parser.rs
```rust
(9, AtnStateKind::RuleStop),
] {
assert_eq!(atn.add_state(kind, Some(0)).expect("state").index(), state);
}
atn.set_left_recursive_rule(0)
.expect("left-recursive rule start");
atn.set_precedence_rule_decision(2)
.expect("precedence decision");
atn.set_loop_back_state(8, 7).expect("loop-back state");
atn.set_rule_to_start_state(vec![0])
.expect("rule start states");
atn.set_rule_to_stop_state(vec![9])
.expect("rule stop states");
for state in [1, 2, 3] {
atn.add_decision_state(state).expect("decision state");
}
for (source, target) in [(0, 1), (2, 3), (2, 8), (7, 2), (8, 9)] {
atn.add_transition(source, ParserTransitionSpec::Epsilon { target })
.expect("epsilon transition");
}
for (source, target, label) in [(1, 2, 1), (1, 2, 2), (4, 6, 4), (5, 6, 3), (6, 7, 1)] {Found a 25 line (193 tokens) duplication in the following files:
let mut atn = ParserAtnBuilder::new(1);
for (state_number, kind) in [
(0, AtnStateKind::RuleStart),
(1, AtnStateKind::StarLoopEntry),
(2, AtnStateKind::Basic),
(3, AtnStateKind::Basic),
(4, AtnStateKind::StarLoopBack),
(5, AtnStateKind::LoopEnd),
(6, AtnStateKind::RuleStop),
] {
assert_eq!(
atn.add_state(kind, Some(0)).expect("state").index(),
state_number
);
}
atn.set_rule_to_start_state(vec![0])
.expect("rule start states");
atn.set_rule_to_stop_state(vec![6])
.expect("rule stop states");
atn.add_decision_state(1).expect("decision state");
atn.set_loop_back_state(5, 4).expect("loop back state");
atn.add_transition(0, ParserTransitionSpec::Epsilon { target: 1 })
.expect("entry transition");
atn.add_transition(1, ParserTransitionSpec::Epsilon { target: 2 })
.expect("loop body");
```rust
---
Found a 26 line (153 tokens) duplication in the following files:
* Starting at line 331 of crates/antlr-rust-runtime/src/atn/lexer.rs
* Starting at line 756 of crates/antlr-rust-runtime/src/atn/lexer.rs
```rust
pub fn next_token_with_hooks<I, A, P, E>(
lexer: &mut BaseLexer<I>,
sink: &mut TokenSink<'_>,
atn: &LexerAtn,
mut custom_action: A,
mut semantic_predicate: P,
mut accept_adjuster: E,
) -> Result<TokenId, TokenStoreError>
where
I: CharStream,
A: FnMut(&mut BaseLexer<I>, LexerCustomAction),
P: FnMut(&BaseLexer<I>, LexerPredicate) -> bool,
E: FnMut(&mut BaseLexer<I>, i32, usize),
{
next_token_with_hooks_impl(
lexer,
sink,
atn,
&mut custom_action,
&mut semantic_predicate,
&mut |_| {},
&mut accept_adjuster,
&mut |_, _| {},
LexerMatchStrategy {
compiled: None,
use_cache: false,Found a 27 line (145 tokens) duplication in the following files:
fn generated_match_token_recovers_missing_token_from_context_follow() {
let atn = generated_match_recovery_atn();
let data = RecognizerData::new(
"Mini.g4",
Vocabulary::new(
[None, Some("'X'"), Some("'Y'")],
[None, Some("X"), Some("Y")],
[None::<&str>, None, None],
),
);
let mut parser = BaseParser::new(
CommonTokenStream::new(Source {
tokens: vec![TestToken::eof("parser-test", 3, 1, 3)],
index: 0,
}),
data,
);
parser.rule_context_stack = vec![
RuleContextFrame {
rule_index: 0,
invoking_state: 0,
},
RuleContextFrame {
rule_index: 1,
invoking_state: 1,
},
];
```rust
---
Found a 25 line (142 tokens) duplication in the following files:
* Starting at line 464 of crates/antlr-rust-runtime/src/atn/lexer.rs
* Starting at line 573 of crates/antlr-rust-runtime/src/atn/lexer.rs
```rust
atn: &LexerAtn,
hooks: &mut H,
) -> Result<TokenId, TokenStoreError>
where
I: CharStream,
H: SemanticHooks,
{
let hooks = RefCell::new(hooks);
let token = next_token_with_hooks_impl(
lexer,
sink,
atn,
&mut |lexer, action| {
let _ = dispatch_lexer_action_hook(&hooks, lexer, action);
},
&mut |lexer, predicate| {
dispatch_lexer_predicate_hook(&hooks, lexer, predicate).unwrap_or(true)
},
&mut |lexer| dispatch_lexer_before_token_hook(&hooks, lexer),
&mut |_, _, _| {},
&mut |lexer, accept_position| {
dispatch_lexer_after_accept_hook(&hooks, lexer, accept_position);
},
LexerMatchStrategy {
compiled: None,Found a 23 line (133 tokens) duplication in the following files:
let source_has_semantic_context = dfa_state_has_semantic_context;
for config in active {
let Some(state) = atn.state(config.state) else {
continue;
};
for transition in &state.transitions {
if !transition.matches(symbol, MIN_CHAR_VALUE, MAX_CHAR_VALUE) {
continue;
}
let mut advanced = config.clone();
set_config_state(atn, &mut advanced, transition.target());
if symbol == EOF {
advanced.consumed_eof = true;
} else {
advanced.position += 1;
}
next.push(advanced);
}
}
let closure = epsilon_closure_with_lexer(lexer, atn, next, semantic_predicate);
let target_has_semantic_context = closure.has_semantic_context;
let suppress_edge = source_has_semantic_context || target_has_semantic_context;
```rust
---
Found a 18 line (128 tokens) duplication in the following files:
* Starting at line 16302 of crates/antlr-rust-runtime/src/parser.rs
* Starting at line 16327 of crates/antlr-rust-runtime/src/parser.rs
```rust
fn epsilon_cycle_atn() -> Atn {
let mut atn = ParserAtnBuilder::new(1);
for (state_number, kind) in [
(0, AtnStateKind::RuleStart),
(1, AtnStateKind::Basic),
(2, AtnStateKind::RuleStop),
] {
assert_eq!(
atn.add_state(kind, Some(0)).expect("state").index(),
state_number
);
}
atn.set_rule_to_start_state(vec![0])
.expect("rule start states");
atn.set_rule_to_stop_state(vec![2])
.expect("rule stop states");
atn.add_transition(0, ParserTransitionSpec::Epsilon { target: 1 })
.expect("transition");Found a 27 line (127 tokens) duplication in the following files:
let mut atn = ParserAtnBuilder::new(2);
assert_eq!(
atn.add_state(AtnStateKind::RuleStart, Some(0))
.expect("state")
.index(),
0
);
assert_eq!(
atn.add_state(AtnStateKind::BlockStart, Some(0))
.expect("state")
.index(),
1
);
assert_eq!(
atn.add_state(AtnStateKind::Basic, Some(0))
.expect("state")
.index(),
2
);
assert_eq!(
atn.add_state(AtnStateKind::Basic, Some(0))
.expect("state")
.index(),
3
);
assert_eq!(
atn.add_state(AtnStateKind::BlockEnd, Some(0))
```rust
---
Found a 22 line (125 tokens) duplication in the following files:
* Starting at line 16783 of crates/antlr-rust-runtime/src/parser.rs
* Starting at line 16855 of crates/antlr-rust-runtime/src/parser.rs
```rust
atn.add_state(AtnStateKind::BlockEnd, Some(0))
.expect("state")
.index(),
4
);
assert_eq!(
atn.add_state(AtnStateKind::RuleStop, Some(0))
.expect("state")
.index(),
5
);
atn.set_rule_to_start_state(vec![0])
.expect("rule start states");
atn.set_rule_to_stop_state(vec![5])
.expect("rule stop states");
atn.add_decision_state(1).expect("decision state");
atn.add_transition(0, ParserTransitionSpec::Epsilon { target: 1 })
.expect("transition");
atn.add_transition(
1,
ParserTransitionSpec::Atom {
target: 2,Found a 15 line (124 tokens) duplication in the following files:
fn context_prediction_reports_context_sensitivity_for_dfa_conflict() {
let atn = two_token_decision_atn();
let mut simulator = ParserAtnSimulator::new(&atn);
let mut workspace = PredictionWorkspace::default();
let mut start_configs = AtnConfigSet::new();
start_configs.add(
AtnConfig::new(2, 1, EMPTY_CONTEXT, &simulator.store.contexts),
&mut simulator.store.contexts,
&mut workspace,
);
let start =
simulator.store.decision_to_dfa[0].add_state(DfaStateBuilder::new(start_configs));
simulator.store.decision_to_dfa[0].set_start_state(start);
let mut accept_configs = AtnConfigSet::new();
```rust
---
Found a 18 line (122 tokens) duplication in the following files:
* Starting at line 4279 of crates/antlr-rust-runtime/src/atn/parser.rs
* Starting at line 4430 of crates/antlr-rust-runtime/src/atn/parser.rs
```rust
atn.set_rule_to_stop_state(vec![7])
.expect("rule stop states");
atn.add_decision_state(1).expect("decision state");
atn.add_transition(0, ParserTransitionSpec::Epsilon { target: 1 })
.expect("transition");
atn.add_transition(1, ParserTransitionSpec::Epsilon { target: 2 })
.expect("transition");
atn.add_transition(1, ParserTransitionSpec::Epsilon { target: 4 })
.expect("transition");
atn.add_transition(
2,
ParserTransitionSpec::Atom {
target: 3,
label: 1,
},
)
.expect("transition");
atn.add_transition(3, ParserTransitionSpec::Epsilon { target: 6 })Found a 20 line (120 tokens) duplication in the following files:
Self::Range { start, stop, .. } => (*start..=*stop).contains(&symbol),
Self::Set { set, .. } => set.contains(symbol),
Self::NotSet { set, .. } => {
(min_vocabulary..=max_vocabulary).contains(&symbol) && !set.contains(symbol)
}
Self::Wildcard { .. } => (min_vocabulary..=max_vocabulary).contains(&symbol),
Self::Epsilon { .. }
| Self::Rule { .. }
| Self::Predicate { .. }
| Self::Action { .. }
| Self::Precedence { .. } => false,
}
}
}
/// Ordered set of integer intervals used by set and negated-set transitions.
///
/// Unicode grammars can contain very large ranges, so this stores normalized
/// intervals rather than expanding every code point into a flat set.
#[derive(Clone, Debug, Default, Eq, PartialEq)]
```rust
---
Found a 34 line (119 tokens) duplication in the following files:
* Starting at line 10886 of crates/antlr-rust-runtime/src/parser.rs
* Starting at line 10961 of crates/antlr-rust-runtime/src/parser.rs
```rust
outcomes.extend(
self.recognize_state(
atn,
RecognizeRequest {
state_number: *target,
stop_state,
index,
rule_start_index,
decision_start_index: next_decision_start_index,
init_action_rules,
predicates,
semantics,
rule_args,
member_actions,
return_actions,
local_int_arg,
member_values: member_values.clone(),
return_values: return_values.clone(),
rule_alt_number: next_alt_number,
track_alt_numbers,
consumed_eof,
committed_decision: transition_committed,
precedence,
depth: depth + 1,
recovery_symbols: epsilon_recovery_symbols.clone(),
recovery_state: epsilon_recovery_state,
},
visiting,
memo,
expected,
)
.into_iter()
.map(|mut outcome| {
prepend_decision(&mut outcome, decision);Found a 22 line (117 tokens) duplication in the following files:
atn: &LexerAtn,
mut custom_action: A,
mut semantic_predicate: P,
mut accept_adjuster: E,
) -> Result<TokenId, TokenStoreError>
where
I: CharStream,
A: FnMut(&mut BaseLexer<I>, LexerCustomAction),
P: FnMut(&BaseLexer<I>, LexerPredicate) -> bool,
E: FnMut(&mut BaseLexer<I>, i32, usize),
{
next_token_with_hooks_impl(
lexer,
sink,
atn,
&mut custom_action,
&mut semantic_predicate,
&mut |_| {},
&mut accept_adjuster,
&mut |_, _| {},
LexerMatchStrategy {
compiled: None,
```rust
---
Found a 13 line (117 tokens) duplication in the following files:
* Starting at line 145 of crates/antlr-rust-runtime/src/parser.rs
* Starting at line 172 of crates/antlr-rust-runtime/src/parser.rs
```rust
ordinary $parser:ident, $state:expr, $rule:expr, $allow_fallback:expr,
$atn:expr, $fatal:path;
retry [$($retry:tt)*];
bind ($ctx:ident, $rule_start:ident, $consumed_eof:ident, $sync_error:ident);
setup { $($setup:tt)* }
body { $($body:tt)* }
success { $($success:tt)* }
recovery { $($recovery:tt)* }
) => {
$crate::__antlr4_rust_generated_rule! {
@body
parser $parser;
enter $parser.base.enter_rule($state, $rule);Found a 24 line (113 tokens) duplication in the following files:
impl IntStream for LookaheadIntStream {
fn consume(&mut self) {
if self.la(1) != TOKEN_EOF {
self.index += 1;
}
}
fn la(&mut self, offset: isize) -> i32 {
if offset <= 0 {
return 0;
}
let offset = offset.cast_unsigned() - 1;
self.symbols
.get(self.index + offset)
.copied()
.unwrap_or(TOKEN_EOF)
}
fn index(&self) -> usize {
self.index
}
fn seek(&mut self, index: usize) {
self.index = index.min(self.symbols.len());
```rust
---
Found a 15 line (113 tokens) duplication in the following files:
* Starting at line 18288 of crates/antlr-rust-runtime/src/parser.rs
* Starting at line 18664 of crates/antlr-rust-runtime/src/parser.rs
```rust
fn generated_match_token_counts_single_token_deletion_recovery() {
let atn = generated_match_recovery_atn();
let data = RecognizerData::new(
"Mini.g4",
Vocabulary::new(
[None, Some("'X'"), Some("'Y'"), Some("'Z'")],
[None, Some("X"), Some("Y"), Some("Z")],
[None::<&str>, None, None, None],
),
);
let mut parser = BaseParser::new(
CommonTokenStream::new(Source {
tokens: vec![
TestToken::new(3).with_text("z"),
TestToken::new(2).with_text("y"),Found a 18 line (112 tokens) duplication in the following files:
(4, AtnStateKind::Basic, 0),
(5, AtnStateKind::RuleStop, 0),
(6, AtnStateKind::RuleStart, 1),
(7, AtnStateKind::Basic, 1),
(8, AtnStateKind::RuleStop, 1),
] {
assert_eq!(
atn.add_state(kind, Some(rule_index))
.expect("state")
.index(),
state_number
);
}
atn.set_rule_to_start_state(vec![0, 6])
.expect("rule start states");
atn.set_rule_to_stop_state(vec![5, 8])
.expect("rule stop states");
atn.add_decision_state(2).expect("decision state");
```rust
---
Found a 12 line (112 tokens) duplication in the following files:
* Starting at line 15355 of crates/antlr-rust-runtime/src/parser.rs
* Starting at line 15438 of crates/antlr-rust-runtime/src/parser.rs
```rust
let mut atn = ParserAtnBuilder::new(1);
for (state, kind, rule) in [
(0, AtnStateKind::RuleStart, 0),
(1, AtnStateKind::StarLoopEntry, 0),
(2, AtnStateKind::Basic, 0), // ops hub
(3, AtnStateKind::Basic, 0), // shift prec
(4, AtnStateKind::Basic, 0), // shift first >
(5, AtnStateKind::Basic, 0), // shift second >
(6, AtnStateKind::Basic, 0), // rel prec
(7, AtnStateKind::Basic, 0), // rel >
(8, AtnStateKind::LoopEnd, 0),
(9, AtnStateKind::RuleStop, 0),Found a 22 line (112 tokens) duplication in the following files:
fn predicate_after_token_atn() -> Atn {
let mut atn = ParserAtnBuilder::new(2);
assert_eq!(
atn.add_state(AtnStateKind::RuleStart, Some(0))
.expect("state")
.index(),
0
);
assert_eq!(
atn.add_state(AtnStateKind::Basic, Some(0))
.expect("state")
.index(),
1
);
assert_eq!(
atn.add_state(AtnStateKind::Basic, Some(0))
.expect("state")
.index(),
2
);
assert_eq!(
atn.add_state(AtnStateKind::Basic, Some(0))
```rust
---
Found a 22 line (111 tokens) duplication in the following files:
* Starting at line 15177 of crates/antlr-rust-runtime/src/parser.rs
* Starting at line 17303 of crates/antlr-rust-runtime/src/parser.rs
* Starting at line 17790 of crates/antlr-rust-runtime/src/parser.rs
```rust
fn left_recursive_loop_with_caller_follow_atn(caller_symbol: i32) -> Atn {
let mut atn = ParserAtnBuilder::new(2);
assert_eq!(
atn.add_state(AtnStateKind::RuleStart, Some(0))
.expect("state")
.index(),
0
);
assert_eq!(
atn.add_state(AtnStateKind::Basic, Some(0))
.expect("state")
.index(),
1
);
assert_eq!(
atn.add_state(AtnStateKind::Basic, Some(0))
.expect("state")
.index(),
2
);
assert_eq!(
atn.add_state(AtnStateKind::RuleStart, Some(1))Found a 14 line (110 tokens) duplication in the following files:
fn parser_matches_token_and_reports_mismatch() {
let source = Source {
tokens: vec![
TestToken::new(1).with_text("x"),
TestToken::eof("parser-test", 1, 1, 1),
],
index: 0,
};
let data = RecognizerData::new(
"Mini.g4",
Vocabulary::new([None, Some("'x'")], [None, Some("X")], [None::<&str>, None]),
);
let mut parser = BaseParser::new(CommonTokenStream::new(source), data);
let matched = parser.match_token(1).expect("token 1 should match");
```rust
---
Found a 13 line (109 tokens) duplication in the following files:
* Starting at line 2067 of crates/antlr-rust-runtime/src/lexer.rs
* Starting at line 2093 of crates/antlr-rust-runtime/src/lexer.rs
```rust
let mut lexer = BaseLexer::new(InputStream::new("β"), data);
lexer.consume_char();
let mut store = TokenStore::new(lexer.source_text(), lexer.source_name());
let mut sink = TokenSink::new(&mut store);
let id = lexer.eof_token(&mut sink).expect("test token should fit");
let token = sink.view(id).expect("emitted token should exist");
// byte_span is the field this test exists to pin and is absent from TokenView's Debug, so
// snapshot the explicit (start, stop, text, byte_span) record rather than the token.
insta::assert_compact_debug_snapshot!(
(token.start(), token.stop(), token.text(), token.byte_span()),
@r#"(1, 0, Some("<EOF>"), Some(2..2))"#Found a 13 line (109 tokens) duplication in the following files:
fn parser_matches_token_and_reports_mismatch() {
let source = Source {
tokens: vec![
TestToken::new(1).with_text("x"),
TestToken::eof("parser-test", 1, 1, 1),
],
index: 0,
};
let data = RecognizerData::new(
"Mini.g4",
Vocabulary::new([None, Some("'x'")], [None, Some("X")], [None::<&str>, None]),
);
let mut parser = BaseParser::new(CommonTokenStream::new(source), data);
```rust
---
Found a 22 line (108 tokens) duplication in the following files:
* Starting at line 8676 of crates/antlr-rust-runtime/src/parser.rs
* Starting at line 9067 of crates/antlr-rust-runtime/src/parser.rs
```rust
) -> Option<RecognizeOutcome> {
let (error_index, message) = self.expected_error_message(rule_index, start_index, expected);
let diagnostic = diagnostic_for_token(self.token_at(error_index), message);
let mut next_index = error_index;
loop {
let symbol = self.token_type_at(next_index);
if sync_symbols.contains(&symbol) {
if next_index == error_index {
return None;
}
break;
}
if symbol == TOKEN_EOF {
break;
}
let after = self.consume_index(next_index, symbol);
if after == next_index {
break;
}
next_index = after;
}
let mut nodes = NodeSeqId::EMPTY;Found a 15 line (108 tokens) duplication in the following files:
fn outcome_ties_keep_later_non_recursive_alternative() {
let arena = RecognitionArena::default();
let first = RecognizeOutcome {
index: 1,
consumed_eof: false,
alt_number: 0,
member_values: MemberEnv::new(),
return_values: BTreeMap::new(),
diagnostics: DiagnosticSeqId::EMPTY,
decisions: Vec::new(),
actions: vec![ParserAction::new(1, 0, 0, None)],
nodes: NodeSeqId::EMPTY,
};
let second = RecognizeOutcome {
actions: vec![ParserAction::new(2, 0, 0, None)],
```rust
---
Found a 13 line (107 tokens) duplication in the following files:
* Starting at line 3111 of crates/antlr-rust-runtime/src/atn/lexer.rs
* Starting at line 3368 of crates/antlr-rust-runtime/src/atn/lexer.rs
```rust
let mut hooks = LifecycleRecordingHooks::default();
let mut store = TokenStore::new(lexer.source_text(), lexer.source_name());
let mut sink = TokenSink::new(&mut store);
let mut ids = Vec::new();
for _ in 0..3 {
let id = if compiled {
next_token_compiled_with_semantic_hooks(
&mut lexer, &mut sink, &atn, &dfa, &mut hooks,
)
} else {
next_token_with_semantic_hooks(&mut lexer, &mut sink, &atn, &mut hooks)
}
.expect("lifecycle token should fit");Found a 17 line (107 tokens) duplication in the following files:
let report_unrecovered_error = self.is_top_level_entry();
let start_state = atn.rule_to_start_state().get(rule_index).ok_or_else(|| {
AntlrError::Unsupported(format!("rule {rule_index} has no start state"))
})?;
let stop_state = atn
.rule_to_stop_state()
.get(rule_index)
.filter(|state| *state != usize::MAX)
.ok_or_else(|| {
AntlrError::Unsupported(format!("rule {rule_index} has no stop state"))
})?;
let start_index = self.current_visible_index();
self.clear_prediction_diagnostics();
self.reset_per_parse_caches();
self.reset_recognition_arena();
let caller_follow_state = self.pending_invoking_follow_state(atn);
```rust
---
Found a 15 line (106 tokens) duplication in the following files:
* Starting at line 2685 of crates/antlr-rust-runtime/src/atn/lexer.rs
* Starting at line 2733 of crates/antlr-rust-runtime/src/atn/lexer.rs
```rust
(4, AtnStateKind::Basic, Some(1)),
(5, AtnStateKind::RuleStop, Some(1)),
] {
let mut state = LexerAtnState::new(state_number, kind);
if let Some(rule_index) = rule_index {
state = state.with_rule_index(rule_index);
}
atn.add_state(state);
}
atn.state_mut(0)
.expect("token start")
.add_transition(LexerTransition::Epsilon { target: 1 });
atn.state_mut(0)
.expect("token start")
.add_transition(LexerTransition::Epsilon { target: 3 });Found a 15 line (104 tokens) duplication in the following files:
impl ParserTransitionData<'_> {
pub const fn target(self) -> usize {
match self {
Self::Epsilon { target }
| Self::Atom { target, .. }
| Self::Range { target, .. }
| Self::Set { target, .. }
| Self::NotSet { target, .. }
| Self::Wildcard { target }
| Self::Rule { target, .. }
| Self::Predicate { target, .. }
| Self::Action { target, .. }
| Self::Precedence { target, .. } => target,
}
}
```rust
---
Found a 13 line (104 tokens) duplication in the following files:
* Starting at line 15290 of crates/antlr-rust-runtime/src/parser.rs
* Starting at line 16694 of crates/antlr-rust-runtime/src/parser.rs
```rust
fn labeled_left_recursive_operator_atn() -> Atn {
let mut atn = ParserAtnBuilder::new(4);
for (state, kind) in [
(0, AtnStateKind::RuleStart),
(1, AtnStateKind::BlockStart),
(2, AtnStateKind::StarLoopEntry),
(3, AtnStateKind::StarBlockStart),
(4, AtnStateKind::Basic),
(5, AtnStateKind::Basic),
(6, AtnStateKind::Basic),
(7, AtnStateKind::StarLoopBack),
(8, AtnStateKind::LoopEnd),
(9, AtnStateKind::RuleStop),Found a 13 line (100 tokens) duplication in the following files:
let mut expected = BTreeSet::new();
for index in (1..self.rule_context_stack.len()).rev() {
let invoking_state = self.rule_context_stack[index].invoking_state;
let Ok(state_number) = usize::try_from(invoking_state) else {
continue;
};
let Some(Transition::Rule { follow_state, .. }) = atn
.state(state_number)
.and_then(|state| state.transitions().first())
.map(ParserTransition::data)
else {
continue;
};
```rust |
|
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📝 WalkthroughWalkthroughThe change adds tail-call metadata to lexer and parser ATNs, validates packed parser ATN format 3, reuses safe lexer contexts, and adds configurable parser handling. Runtime code-generation compatibility advances to revision 14 while revisions 12 and 13 remain supported. ChangesTail-call support
Estimated code review effort: 4 (Complex) | ~60 minutes Mergeability Score: 🟡 Moderate · up to This change can incorrectly alter parser prediction for merged contexts that still contain an empty return path, potentially producing incorrect parsing under the conservative SLL policy. The PR is not merge-ready until the guard is corrected and covered by a regression test. Possibly related PRs
🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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Inline comments:
In `@crates/antlr-rust-runtime/src/atn/mod.rs`:
- Around line 54-56: Update plain_epsilon_tail_call to accept a caller-owned
marks buffer and clear/reinitialize it at the start of each call instead of
allocating a new vector. Add one reusable Vec<u8> per classification loop in
LexerAtn::identify_tail_calls and ParserAtnBuilder::mark_tail_calls, passing it
through every transition while preserving the existing traversal behavior.
- Around line 193-222: Document on identify_tail_calls that it must be called
only after all transitions and rule-return edges have been added, and must be
called again after any subsequent graph mutation through add_state,
add_transition, or state_mut. Keep the implementation unchanged.
In `@crates/antlr-rust-runtime/src/atn/parser.rs`:
- Around line 2252-2262: Update the conservative tail-call guard in the parser
transition logic to use contexts.has_empty_path(config.context) instead of
contexts.is_empty(config.context), so merged contexts containing an empty path
retain the return frame; leave the reduced-accuracy branch unchanged. Add a case
to marked_tail_calls_reuse_contexts_under_the_selected_sll_policy covering a
merged context with an empty path and assert that conservative mode preserves
the return frame.
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⛔ Files ignored due to path filters (11)
crates/antlr-rust-codegen/src/generator/snapshots/antlr_rust_codegen__generator__tests__generated_module_file_header.snapis excluded by!**/*.snapcrates/antlr-rust-codegen/tests/antlr4_rust_gen_cli/snapshots/antlr4_rust_gen_cli__cli__generated_codegen_api_checks.snapis excluded by!**/*.snapcrates/antlr-rust-codegen/tests/antlr4_rust_gen_cli/snapshots/antlr4_rust_gen_cli__cli__generated_codegen_api_mismatch_diagnostic.snapis excluded by!**/*.snapcrates/antlr-rust-g4-parser/src/generated/antlr_v4_lexer.rsis excluded by!**/generated/**crates/antlr-rust-g4-parser/src/generated/antlr_v4_parser.rsis excluded by!**/generated/**crates/antlr-rust-rs-parser/src/generated/rust_lexer.rsis excluded by!**/generated/**crates/antlr-rust-rs-parser/src/generated/rust_parser.rsis excluded by!**/generated/**crates/antlr-rust-runtime/src/xpath/generated/x_path_lexer.rsis excluded by!**/generated/**crates/antlr-rust-toml-parser/src/generated/toml_lexer.rsis excluded by!**/generated/**crates/antlr-rust-toml-parser/src/generated/toml_parser.rsis excluded by!**/generated/**docs/migration.mdis excluded by!**/docs/**
📒 Files selected for processing (12)
README.mdcrates/antlr-rust-codegen/src/grammar/atn/lexer.rscrates/antlr-rust-codegen/tests/antlr4_rust_gen_cli/cli.rscrates/antlr-rust-runtime/src/atn/lexer.rscrates/antlr-rust-runtime/src/atn/mod.rscrates/antlr-rust-runtime/src/atn/parser.rscrates/antlr-rust-runtime/src/atn/parser_atn.rscrates/antlr-rust-runtime/src/atn/serialized.rscrates/antlr-rust-runtime/src/lexer.rscrates/antlr-rust-runtime/src/lib.rscrates/antlr-rust-runtime/src/parser.rsthird_party/antlr-v4-grammar/self-hosted.sha256
Keep prediction return contexts one-to-one with semantic rule-call provenance when parameterized predicates enable call tracking. Otherwise a tail-elided nested call can jump over its caller stop and leave a stale active rule in later predicate evaluation. Add a closure-level regression that reproduces the stale provenance and verifies predicates reached after both returns inherit no tail-called rule path.
📊 Source Code Metrics (this PR vs
|
| File | Cyclomatic | Cognitive | Functions | LLOC | MI |
|---|---|---|---|---|---|
| crates/antlr-rust-runtime/src/parser.rs | 2451 (main: 2446) 🔴 | 1618 (main: 1614) 🔴 | 787 (main: 785) 🔴 | 5495 (main: 5475) 🔴 | 0 ⚪ |
| crates/antlr-rust-runtime/src/atn/parser_atn.rs | 665 (main: 628) 🔴 | 353 (main: 308) 🔴 | 211 (main: 204) 🔴 | 1034 (main: 926) 🔴 | 0 ⚪ |
| crates/antlr-rust-runtime/src/lexer.rs | 337 (main: 336) 🔴 | 76 ⚪ | 207 (main: 206) 🔴 | 571 (main: 570) 🔴 | 0 ⚪ |
| crates/antlr-rust-runtime/src/atn/parser.rs | 459 (main: 438) 🔴 | 317 (main: 309) 🔴 | 151 (main: 142) 🔴 | 1370 (main: 1262) 🔴 | 0 ⚪ |
| crates/antlr-rust-runtime/src/atn/lexer.rs | 476 (main: 467) 🔴 | 353 (main: 347) 🔴 | 124 (main: 120) 🔴 | 1056 (main: 1030) 🔴 | 0 ⚪ |
| crates/antlr-rust-codegen/src/grammar/atn/lexer.rs | 374 ⚪ | 239 ⚪ | 67 ⚪ | 538 (main: 537) 🔴 | 0 ⚪ |
| crates/antlr-rust-runtime/src/atn/mod.rs | 93 (main: 55) 🔴 | 44 (main: 13) 🔴 | 41 (main: 34) 🔴 | 125 (main: 57) 🔴 | 0 (main: 7.23) 🔴 |
| crates/antlr-rust-runtime/src/atn/serialized.rs | 298 ⚪ | 217 ⚪ | 36 ⚪ | 305 (main: 304) 🔴 | 0 ⚪ |
| crates/antlr-rust-runtime/src/lib.rs | 4 ⚪ | 3 ⚪ | 1 ⚪ | 7 ⚪ | 29.36 (main: 29.44) 🔴 |
Generated by mehen v1.8.1 — the code quality watcher.
Reuse traversal marks, work, and successor buffers across rule-transition classification instead of allocating them for every candidate. Document that lexer markers must be recomputed after graph mutation. Pin the fork-compatible empty-local-context behavior: SLL wildcard merges collapse empty paths to the local empty context, while full-context arrays with an empty path remain eligible for tail-call elimination.
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Use allocation-free structural tail-call flag validation for trusted generator-emitted static tables, preserving ParserAtn::from_static's initialization contract. Continue recomputing every derived marker for owned/deserialized streams, including the builder path that proves generated data before rendering. Exercise the static path with a format-3 ATN containing a marked rule transition while retaining full derived-marker corruption tests through from_owned.
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Retain return frames for every full-context path containing an empty branch; only explicit reduced-accuracy SLL may elide those contexts. This keeps full-context alternatives converged at their enclosing rule state. Do not mark reduced-SLL tail calls as reaching outer context at call entry. Let closure set that marker only after the callee reaches its stop, preventing a mismatching callee from becoming a false accepting alternative. Add regressions for both cases.
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Summary
the enclosing rule stop through plain epsilon transitions
conservative SLL behavior by default
caller context
generated-code API to revision 14 while retaining revisions 12 and 13
Compatibility
Packed parser ATN formats 1 and 2 remain readable. Revision-12 and revision-13
generated recognizers continue to compile because the runtime retains every API
surface and metadata format they require.
Generated static parser tables keep allocation-free structural validation.
Owned/deserialized streams still recompute every derived tail-call marker, so
the builder proves generated format-3 data before it is rendered.
The less-accurate SLL policy is explicit through
ParserAtnSimulator::new_with_tail_call_preserves_sll(..., false)(and itsshared-cache counterpart). Conservative and compact modes use separate shared
DFA stores. Full-context prediction always retains contexts containing an empty
path, and reduced SLL records outer-context completion only after the elided
callee actually reaches its stop state.
When parameterized predicates enable semantic rule-call provenance tracking,
the parser retains marked return frames so context pops and provenance pops
remain one-to-one.
Checked-in artifact effect
and still derives its one applicable tail call for ATN fallback paths
No parse-time speedup is claimed without benchmark evidence.
Validation
cargo clippy --locked --workspace --all-targets --all-features -- -D warningscargo test --locked --workspace --all-featurestools/grammar-frontend/update-stage0.sh --updatetools/rust-syntax/update-generated.sh --checktools/toml-syntax/update-generated.sh --checkcargo run --release --quiet -p antlr-rust-runtime-testsuite --bin antlr4-runtime-testsuiteCloses #336